Researchers from the University of Wisconsin measured the rate of specialization — meaning an athlete significantly sacrificed time with friends or family or participation in other sports — among 1,544 athletes in Wisconsin and tracked lower-extremity injuries. The study found athletes who specialized suffered those injuries “at significantly higher rates” than those who do not.

“We collected this much data and saw there is something here,” said Tim McGuine, the study’s author and a sports medicine researcher at the University of Wisconsin School of Medicine and Public Health. “It’s pretty striking.”

More than 40 percent of female athletes and 28 percent of male athletes surveyed reported specializing. Soccer was the most-specialized sport. Almost half of the athletes of both genders who reported playing soccer said that was their primary sport.

Muscle or ligament sprains were the most commonly reported injuries, mostly to the ankle or knee, which accounted for 59.4 percent of injuries reported.

Those injuries are a result of overtraining and exposure, McGuine said.

Specialized athletes who play or train for their sport year-round put more stress on a concentrated group of muscles, ligaments and bones related to their sport. A baseball pitcher, for example, places more stress on his elbow and shoulder than abdomen. He is more likely to suffer injuries to his arm than a nonspecialized pitcher because of the stress of training, McGuine said.

He is also more susceptible to injury because he is exposed to that sport more often. In other words, the more you pitch, the more opportunity for things to go wrong, even if they’re not stress-related.

“The more you play at any given activity, the more likely you are to get hurt, just out of exposure,” said William Roberts, a practicing physician and professor of family medicine at the University of Minnesota. “If you play club and high school sports, you play 10 to 12 months out [of] the year; that might be an exposure issue. For kids who play club and high school at the same time, it might be a fatigue issue.”

But the pressure to achieve in a single sport drives some athletes to continue to specialize and overtrain, said Jennifer Rheeling, an athletic trainer with D.C. Public Schools.

She tries to get football players to go out for the basketball team or run track in the spring. She tells sprinters to be wide receivers and high jumpers to play volleyball.

“I think they’re just so concerned that if they take a day off, somebody is going to get ahead of them,” she said. “These kids, they’re so good at football and basketball, they don’t want to be not as good at another sport.”

Roberts and McGuine recommend playing multiple organized sports but one at a time. Don’t train for track and football in the same season, but go ahead and work out for football and play pickup basketball later.

That kind of overtraining led McKinley Tech senior sprinter Denzell Brown into a years’ worth of stress injuries from which he is just now recovering. During the summer between track and football season, he used to wake up at 5 a.m. to do a full sprinter’s workout, go to work, hit the weight room and then do another sprinting or football workout at night.

After all that training, he wondered why he wasn’t seeing the improvement he wanted in either sport. At the D.C. Interscholastic Athletic Association track and field championships his junior season, a calf strain from those workouts, he said, caused him to hobble through the finish line of the 4×400 meter relay.

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“My body was shutting down,” he said after the race.

“I realized I was putting too much stress on my body that I thought was hard work,” Brown says now.

He doesn’t regret specializing, he said — he is on the verge of a Division I track scholarship — but he did more cross-training or took more time off to rest over the past seven months.

McGuine has another suggestion.

“If you want to play basketball over the summer, do it, but don’t play 60 games,” he said. “Pick your spots. Be a swimmer, too.”